Hip Dysplasia

A common cause of Hindlimb lameness and gait abnormality in many breeds of dog.

The word ‘dysplasia’ just means badly formed. This means that the joint is normal at birth and then becomes abnormal over a period of time. In other words dogs are not born with Hip Dysplasia, but they are born with a variable genetic tendency or predisposition to the hip developing abnormally over the period of skeletal development (up to 9-10 months). Some dogs may have no predisposition to developing Hip Dysplasia whilst others may have a significant predisposition. This likelihood of developing Hip Dysplasia is based on the Genetic make up of the dog and this is obviously governed by the “Family Tree” of the dog and the transmission of genetic material between generations. There is however no single Gene for Hip Dysplasia. Instead it is termed polygenic. The genes involved in Hip Dysplasia relate to the genetic influences on Growth Rate and so forth. In particular it is felt that rapid skeletal growth results in the skeleton outgrowing the supporting soft tissues leading to hip laxity (loose hips). Depending on the degree of laxity and the activity of the individual this leads to a braod spectrum of pathologies of the hip joint itself.

The Signs of Hip Dysplasia

In the early stages of Hip Dysplasia, there may be little to see in the way of overt lameness. Instead in this stage it is things like difficulty to rise from sitting or lying or a tendency to “Bunny-Hop” when moving at a trot or faster. Bunny Hopping means running with both hindlimbs close together. Dogs with symmetric bilateral clinical Hip Dysplasia may appear completely normal apart from these signs. This is because dogs can transfer their body weight forward onto the forelimbs without there being any obviously visible change in their appearance. Of course some patients at this early phase may appear subdued and even vocalise in discomfort occasionally. They may prefer to eat whilst lying down and may pull themselves along the floor to reach a distant toy for example. If the signs progress from here owners may begin to see stiffness after rest affecting one limb more than another. Stiffness is a “poverty of action” with reduced flexibility and an appearance similar to that seen in an aged animal.

Over the period between 6 and 8 months, overt asymmetric lameness may be seen. Rarely will this be non-weight bearing lameness but will appear as a shortened stride with variable degrees of reduced load. This may only be noted after exertion or post rest. Acute onset non weight bearing lameness may occur in a small number of patients and the common causes of this are shown in the section below.

Anatomy of the Hip Joint

Acute Lameness in Dysplastic Dogs

Acute Septic Arthritis: Joints that are abnormal, inflamed or degenerate are more likely to be colonised by bacteria that may be in the bloodstream. This must be ruled out by aspirating Synovial Fluid (Joint Fluid) and examining the cells present under a microscope. If infection is suspected the fluid is generally submitted to a Laboratory for Culture and sensitivity.

Acute Round Ligament Rupture: This is the ligament that connects the Head of the Femur (Ball) to the Acetabular Wall (Socket). This becomes stretched as a result of progressive subluxation. Subluxation is best understood as a partial dislocation. In a complete dislocation there is no contact between the joint surfaces. In Subluxation, the degree of contact between opposing joint surfaces is reduced. This process requires stretch of the Round Ligament and the Joint Capsule. As with all physical objects, there is a limit to how far the Round Ligament can stretch before it snaps. If this occurs suddenly, the resulting sprain effect with bleeding into the joint may result in significant discomfort and therefore lameness.

Acute Cranial Cruciate Ligament Rupture: Cruciate pathology is seen in many of the same breeds affected by Hip Dysplasia and it is reasonable to say that Cruciate Pathology is the commonest cause of lameness in dogs with Hip Dysplasia. This must therefore be ruled out in all patients with Hindlimb Lameness, irrespective of the radiographic appearance of the Hips.

I think my dog has Hip Dysplasia

If you have noticed signs in your pet similar to those mentioned above, the best thing to do is to visit your Veterinary Surgeon. They will listen to your description of what you have seen. Before going, why not gather the family together to collate everyone’s observations. Your Vet will then watch your dog walk and perform a gentle examination of your dog. If they are concerned, they may recommend taking X-rays of your dog's hips. Often following this they will send the radiographs to us for evaluation or they may suggest that you come over to see us. Andy Torrington sees most patients with signs or x-rays suggestive of Hip Dysplasia referred to Torrington Orthopaedics. I always think that the earlier we see you and your dog, the better. This way we can chart progress or deterioration together and we can get a management plan under way as soon as possible.

General Advice to Reduce Risks

Moderate Exercise

The soft tissue support for the joints of young dogs is often rather weak. Exercising beyond the fatigue limits of the muscles around the Hip will put more stress on the other support structures such as the Joint Capsule and the Round Ligament. If daily stresses exceed the strength of these important “intrinsic” support structures, they will weaken and stretch. This will result in Hip Laxity (loose hips) and this is the first part of the journey towards Hip Dysplasia often. I would recommend no more than five minutes per month of life as an exercise limit. Periods of enforced rest at home are also useful. Babies are not active all day but have naps and so forth. You should aim to include “down-time” in your pup's day and make sure that activity sessions are enjoyable but not extended.

Nutrition

Do not use Calcium or Vitamin supplements in your pup unless your vet has specifically suggested this (and this should be rarely advised). Do not use diets that are high in calorie or protein content. Try to use a diet with less than 25% protein and generally avoid diets that have the words Active or Growth in their name. Pay attention to your pup’s weight and growth rate. Periods of accelerated growth rate should be managed by reducing activity and seeking advice regarding the plane of nutrition. In most Medium and Large breed dogs, Puppy food is unnecessary in my view.

Avoid Repetitive High Impact Activity

Running up and down stairs repeatedly through the day is probably best avoided as are high impact Agility or Ball type games in growing dogs. Tug-Of-War style play with your dog should be avoided. Periods of play with other dogs should be supervised and limited in the growth phase.

Choosing a Pup

Try to acquire your pup from reputable breeders who have shown diligence regarding monitoring their breeding animals’ Hips by having them Hip Scored. Some breeders are sceptical about this process, but it is the best method we have for establishing the genetic material of the breeding stock. Do not choose the largest puppy in the litter as being overweight at 6-8 weeks has been shown to be a significant risk factor.

Management of Hip Dysplasia

Hip Dysplasia is a term applied to the abnormal development of the Hip Joint, as explained above. The spectrum of the pathology is very broad as is the spectrum of Clinical Signs (“symptoms”). There is little correlation between the visual appearance of the Hips as seen in X-rays and the clinical signs that the patient displays. This lack of correlation is also seen in human Hip pathology. The type of management required for a patient with Hip Dysplasia should always be derived from the Clinical Impact and Never the Radiographic Appearance.

The other variable regarding management is the Stage of Life of the patient. That is not to say that we should treat old dogs in a different way from younger dogs because of their age but because the lameness derived from Hip pathology may be diffferent at these different life stages. As indicated above, young dogs (under 10 months) may experience significant discomfort from the fatigue and stretch of the soft tissues. In some patients in this stage, restricted activity and judicious pain relief and supportive therapy may permit significant clinical improvement. In older patients with Hip pain secondary to Hip Dysplasia, the source of discomfort is more likely to be the result of painful contact between the surfaces of the hip (Femur and Acetabulum or Ball and Socket). For those patients, other options may be indicated.

Medical and Supportive Therapies

This form of management is often used in young dogs with Hip Dysplasia. The aim of this therapy in younger patients is “bridge” a period of difficulty. As such it is a temporary measure used to permit reduced discomfort during the approach to maturity. Some patients may show sufficient improvement as their body matures to have a normal or near-normal quality of life as adults with this approach. It is generally reserved for dogs with mild to moderate signs or in patients where there are factors that may indicate increased risk with surgical options for example. Some of these risk factors are listed below.

Surgical Risk factors in young dogs

Surgical Management Options

The aim of surgery is to resolve pain associated with Hip Dysplasia. Total Hip Replacement is the gold standard therapy in patients that are over six or seven months and has the aims of resolution of discomfort and restoration of perfect Hip Mechanics. Prior to this age there are some surgical options that may be used to improve the congruence (close fitting) and mechanics of the Dysplastic Hip. These can only be used when the degree of secondary pathology is not severe and in many patients this option may be unavailable from the age of five months. Where procedures such as Double Pelvic Osteotomy or Pubic Symphysiodesis are being considered there will always be a thorough evaluation of suitability before proceeding with these. Juvenile Pubic Symphysiodesis is only recommended in pups of less than 22 weeks of age, as after this it will be unlikely to provide any benefit at all.

Procedures such as Femoral Head and Neck Ostectomy (Excision Arthroplasty) will rarely be advised in juvenile patients or in dogs over 15 kg at any age. This procedure may reduce the discomfort associated with painful contact but will result often in long term mechanical dysfunction of the joint.

Total Hip Replacement (THR) is an option in any patient over 7 months. We use the Zurich Cementless Total Hip Replacement system invented by Kyon AG. We have used this system now for over five years and we are very happy with its long term results. Suitability for THR is dependent upon the patient having the key “Inclusion” criterion of Hip Pain and an absence of the “exclusion” criteria. The exclusion criteria are shown below:

The presence of other active Orthopaedic Disease: It is critical that all other active orthopaedic problems such as Cranial Cruciate Disease, Patellar Luxation and so forth are ruled out and/or managed prior to proceeding with THR.

The presence of Neurological Disease: Incoordination presents a clear risk to outcome following THR.

Chronic Infective Foci: This includes Skin Disease, Ear Disease, Anal Sac Disease, Dental Disease and Recurrent Diarrhoea. These would need to be managed before considering a Total Hip Replacement because they increase the risk of infection at the surgical site. If infection occurs, removal of the prostheses (the components of the artificial joint) will almost always be required, as a result we will always check for these issues and either suggest that methods be implemented to control these or may suggest that THR is not a safe option.

Aggression: There is a considerable nursing requirement following THR and aggressive dogs would pose a risk to themselves and staff. For this reason dogs with aggression issues would not be considered suitable candidates. If this is due to fear, then often we can help to resolve this and in many cases have been able to proceed safely with THR.

Poor Patient Compliance: Occasionally young dogs are just too exuberant to be suitable for THR. In most cases though behavioural training will resolve this issue.

Poor Owner Compliance: After coming home, aftercare can be difficult and we rely on owners that understand the importance of their role in a successful outcome. This is rarely an issue.